In recent years the substantial increases in costs of basic materials such as plastics, cement, asphalt and the like has encouraged development and use of filler materials to reduce the amount and cost of the basic materials used and the weight of the finished materials.
The substantial increases in the energy costs of heating and cooling has encouraged the development of new and better insulation materials and many new insulation materials and insulating systems using the new materials have been developed in an attempt to satisfy these needs.
One of the newly suggested filler materials and insulating materials utilizes hollow plastic microspheres. The known methods for producing hollow plastic microspheres, however, have not been successful in producing microspheres of uniform size or uniform thin walls which makes it very difficult to produce filler and insulation materials of controlled and predictable physical and chemical characteristics and quality. Also, the relatively high cost and the relatively small size of the prior art microspheres has limited their use.
One of the existing methods of producing hollow plastic microspheres, for example, as disclosed in the Veatch et al U.S. Pat. No. 2,797,201, is to disperse a liquid or solid gas-phase precursor material in a plastic material to be blown to form the microspheres. The plastic material containing the solid or liquid gas-phase precursor enclosed therein is then heated to convert the solid or liquid gas-phase precursor material into a gas and is further heated to expand the gas and produce the hollow plastic microsphere containing therein the expanded gas. This process is, understandably, difficult to control and inherently produces plastic microspheres of random size and wall thickness, microspheres with walls that have sections or portions of the walls that are relatively thin, walls that have holes, small trapped bubbles, trapped or dissolved solvents or gases, any one or more of which will result in a substantial weakening of the microspheres, and a substantial proportion of the microspheres which are not suitable for use and must be scrapped or recycled.
Further, the use of conventional fiberglass insulation is being questioned in the light of the recently discovered possibility that fiberglass of certain particle size may be carcinogenic in the same or similar manner as asbestos. The use of polyurethane foams, urea-formaldehyde foams and polystyrene foams as insulating materials have recently been criticized because of their dimensional and chemical instability, for example, a tendency to shrink and to evolve the blowing gases such as Freon and to evolve unreacted gases such as formaldehyde.
In addition, in some applications, the use of low density microspheres presents a serious problem because they are difficult to handle since they are readily elutriated and tend to blow about. In situations of this type, the filamented microspheres of the present invention provide a convenient and safe method of handling the microspheres.
Thus, the known methods for producing hollow plastic microspheres have therefore not been successful in producing microspheres of uniform size or uniform thin walls or in producing hollow plastic microspheres of controlled and predictable physical and chemical characteristics, quality and strength or at low cost.